Tectonic processes and hazards

Edexcel Geography A Level

What are the two classifications of tectonic hazards?

seismic and volcanic

Describe the global distribution of earthquakes

The main earthquake zones are found along plate boundaries

Roughly 70% of all earthquakes are found in the Ring of Fire in the Pacific Ocean.

The most powerful are associated with convergent or conservative boundaries but rare intra-plate earthquakes can occur.

Describe the global distribution of tsunamis

• around 90% of all events occur within the Pacific Basin

• Most are generated at subduction zones

What is the oceanic fracture zone (OFZ)

a belt of activity through the oceans along the mid-ocean ridges, coming ashore in Africa, the Red Sea, the Dead Sea Rift and California.

An oceanic fracture zone is a zone of lithospheric weakness generally perpendicular to the axis of the mid oceanic ridge

What is the continental fracture zone (CFZ)

a belt of activity following the mountain ranges from Spain, via the Alps, to the Middle East, the Himalayas to the East Indies and the Pacific.

Where do a small minority of earthquakes occur?

Along old fault lines e.g. the Church Stretton Fault in Shropshire

Define Seismic hazards

generated when rocks within 700km of the Earth’s surface come under such stress that they break and become displaced

Define a volcanic hazard

associated with an eruption event

When does an intra-plate earthquake occur? and why?

In the middle or interior of tectonic plates and are much rarer than boundary earthquakes. The causes of this are not fully understood but it is assumed that plates have pre-existing weaknesses which become reactivated, forming seismic waves. For example, an intraplate earthquake may occur if solid crust, which has weakened overtime, cracks under pressure.

What is a hazard?

a percieved natural event which poses a potential threat to human life and property

What is a volcanic hotspot?

A localised area of the lithosphere (Earth’s crust and upper mantle) which has an unusually high temperature due to the upwelling of hot molten material from the core. Here magma rises as plume (hot rock)

A hotspot is when one of Earth's outer tectonic plates moves over an unusually hot part of the Earth's mantle (magma/mantle plume) and large amounts of magma rise up, piercing through the plates and producing large volcanic eruptions at the Earth’s surface e.g. Kilauea, Hawaii, Yellowstone

Outline how hotspot volcanism has led to the development of the Hawaiian islands. You should refer to examples volcanic activity present in Hawaii and the types of landforms such as shield volcanoes that are produced. How do landscapes such as the Hawaiian islands change over time.

The Hawaiian Islands were formed by such a hot spot occurring in the middle of the Pacific Plate. While the hot spot itself is fixed, the plate is moving. So, as the plate moved over the hot spot, the string of islands that make up the Hawaiian Island chain were formed.

The Hawaiian Islands form an archipelago that extends over a vast area of the North Pacific Ocean. The archipelago is made up of 132 islands, atolls, reefs, shallow banks, shoals, and seamounts stretching over 1,500 miles from the island of Hawaii in the southeast to Kure Atoll in the northwest.

Some volcanic eruptions are 'intra-plate' meaning there are distant from a plate boundary at locations called mid-plate hotspots, such as Hawaii and the Galapagos Islands. 

At these locations:

1. Isolated plumes of convecting heat, called mantle plumes, rise towards the surface, generating basaltic volcanoes that tend to erupt continuously. 

2. A mantle plume is stationary, but the tectonic plate above moves slowly over it. 

3. Over millennia, this produces a chain of volcanic islands, with extinct ones most distant from the plume's location. 

stats on hotspots

About 95% of the world’s volcanoes are located near the boundaries of tectonic plates.

The other 5% are thought to be associated with mantle plumes and hot spots. 

What is a mantle plume?

Where do mantle plumes occur?

areas where heat and/or rocks in the mantle are rising towards the surface. A hot spot is the surface expression of the mantle plume.

Mantle plumes occur where there are rigorous rising convection currents. In some locations these can break through overlying plates to create tectonic activity. Some current hotspots are shown on the map below. Hawaii is the most significant 'intra-plate' example.

Hotspot volcanism

How has it led to the formation of the Hawaiian Islands?

does not occur at the boundaries of Earth’s tectonic plates, where other volcanism occurs.

The mantle plumes that form hotspots are thought to be relatively stationary, while tectonic plates are not.

Once the tectonic plate has moved, the once active volcano is now no longer on top of the mantle plume and so becomes extinct.

What are the characteristics of the different sections of the Earth’s structure?

• Crust: outside layer of earth made of solid rock (basalt and granite)

  • There are two types of crust

    • Oceanic: denser and thinner, mainly basalt

    • Continental: less dense, thicker, mainly granite

• Mantle: below the crust, up to 2900km thick. Consists of hot, dense, iron and magnesium-rich solid rock.

The upper part of the mantle and the crust make up the lithosphere and these are broken up into plates- either oceanic or continental.

Crystals in the transition zone hold as much water as all the oceans on Earth’s surface.- but as hydroxide- how cool!

The Asthenosphere is partially melted- the mechanically weak and ductile region of the upper mantle of earth- below the lithosphere

In between the core and mantle is the Gutenberg discontinuity 2900km- the velocity of seismic waves changes abruptly here

• The core: centre of earth

  • liquid outer- nickel, iron, molten rock

  • solid inner

• Radioactive reactions occur inside the core which produces convection currents in the mantle. This causes the tectonic plates to move.

What was Pangea? and what evidence is there for the fact that the continents we know today as Africa and South America were once joined?

A single supercontinent which comprised of North and South America, Africa and Europe. It was during the late Paleozoic Era until the very late Triassic. 300-200 million years ago. #bringbackPangea2025 #rip

Evidence:

1. Continental/Jigsaw Fit- there is a similarity in the coastlines of eastern south America and west Africa- this best fits at a depth of 1,000 metres below current sea level. Any gaps or overlaps that could disprove this can be explained by coastal erosion, deposition and eustatic and isostatic changes.

2. Geological Fit- Both coastlines have ancient rock outcrops (cratons) over 2,000 million years old of the same rock type. A belt of ancient rocks along the Brazilian coast, for example, matches one in West Africa.

3. Glacial Fit- Indications of widespread glaciation from 380 to 250 million years ago are evident in Antarctica, southern South America, southern Africa, India, and Australia. If these continents were once united around the south polar region, this glaciation would become explicable as a unified sequence of events in time and space. More evidence comes from glacial striations – scratches on the bedrock made by blocks of rock embedded in the ice as the glacier moves. These show the direction of the glacier, and suggest the ice flowed from a single central point.

4. Tectonic Fit- Fragments of an old fold mountain belt between 450 and 400 million years ago are found on widely separated continents today. Pieces of the Caledonian fold mountain belt are found in Greenland, Canada, Ireland, England, Scotland and Scandinavia. When these land masses are re-assembled the mountain belt forms a continuous linear feature.

5. Fossil evidence- The plant Glossopteris is a fern that has been found in Africa, Antarctica, Australia and South America. It is used as evidence that these continents must have at some point around 250 million years ago been joined. Mesosaurus is an extinct reptile that has been found in both Africa and South America. As Mesosaurus was a coastal animal, and therefore could not have+ crossed the Atlantic Ocean

6. Paleomagnetism- see flashcard

7. Marine deposits- Moreover, the earliest marine deposits along the Atlantic coastlines of either South America or Africa are Jurassic in age (approximately 199.6 million to 145.5 million years old), which suggests that the ocean did not exist before that time.

8. Along the Wadati- Benioff foci, the depth of waves shows subduction of the denser basaltic oceanic plates into the upper mantle.

What is Continental drift? Who are some people that came up with and some geophysical evidence used to develop these theories?

The surface of the Earth is split up into a series of tectonic plates. These move across the Earth's surface due to convection currents in the mantle. Where the plates meet or rub against each other mountains and volcanoes may form and earthquakes may happen, sometimes causing huge waves called tsunamis.

• Alfred Wegener's Continental Drift hypothesis in 1912 that postulated that now-separate continents had once been joined. 

• Harry Hess- Sea Floor Spreading- identified mid ocean ridges, new sea floor being created

• The ideas of Arthur Holmes in the 1930s that Earth's internal radioactive heat was that driving force of mantle convection that could move tectonic plates.

• The discovery in 1960 of the asthenosphere, a weak, deformable layer beneath the rigid lithosphere, on which the latter moves.

• The discovery in the 1960s of magnetic strips in the oceanic crust of the sea bed; these are palaeomagnetic signals from past reversals of the Earth's magnetic field and prove that new ocean crust is created by the process of sea-floor spreading at mid-ocean ridges. (seafloor spreading and palaeomagnetism occur at constructive margins, where new crust is being made) Vine and Matthews

• The recognition of transform (conservative- slide) faults and Hotspots by Tuzo Wilson in 1965. 

Describe and explain paleomagnetism

The alternating polarisation of new land created. As magma cools, the magnetic elements within will align with the Earth’s magnetic field, which can alternate over thousands of years. We are due another flip. The climate crisis has an effect here.

Iron particles in lava are aligned with the Earth’s magnetic field. At regular intervals the polarity of the Earth reverses; this results in a series of magnetic stripes with the sea-floor rocks are aligned alternately towards north and south poles. This striped pattern, which is mirrored exactly on either side of a mid-oceanic ridge, suggests that the ocean crust is slowly spreading away from the boundary.

Describe and explain sea floor spreading

a geologic process in which tectonic plates—large slabs of Earth's lithosphere—split apart from each other.

a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.

Which plate boundary type has the deepest focus and highest magnitude earthquakes

destructive will have deepest focus due to subduction along the Benioff zone- also largest magnitude

How does strength of the rock affect the earthquake magnitude and focus?

more seismic energy stored in stronger rocks- locked fault- large magnitude earthquakes when that pressure is released, weaker permeable rocks- more liquefaction

How do seismic waves affect focus and magnitude of earthquakes?

l waves are strongest and most damage due to ground shaking, p waves are the weakest and arrive first (shunting waves)

Describe and explain slab pull

As oceanic lithosphere cools, it becomes denser and thicker. At a convergent plate boundary the oceanic lithosphere sinks beneath the adjacent plate forming an ocean trench and subduction zone. As a result of its own weight, the descending plate is pulled by gravity through the mantle asthenosphere, which is hotter and less rigid. This force is known as slab pull. It is believed to be the major force driving plate motions.

occurs at destructive margins. 

Describe and explain Mantle Convection

Mantle convection describes the movement of the mantle as it transfers heat from the white-hot core to the brittle lithosphere. The mantle is heated from below, cooled from above, and its overall temperature decreases over long periods of time. All these elements contribute to mantle convection.

Convection currents transfer hot, buoyant magma to the lithosphere at plate boundaries and hot spots. Convection currents also transfer denser, cooler material from the crust to Earth’s interior through the process of subduction.

Earth's heat budget, which measures the flow of thermal energy from the core to the atmosphere, is dominated by mantle convection. Earth’s heat budget drives most geologic processes on Earth, although its energy output is dwarfed by solar radiation at the surface.

It was long thought that this resulted in convection currents in the mantle which were responsible for the movement of tectonic plates across the Earth’s surface – indeed this is still the most common idea illustrated in many textbooks and on the internet. However, this theory is now largely out of favour, with modern imaging techniques unable to identify mantle convection cells that are sufficiently large to drive plate movement. Some plate models show that two thirds of the Earth’s surface move faster than the underlying mantle so there appears to be little or no evidence that convection currents in the mantle move plates (apart maybe from some very small plates in unusual circumstances).

Describe and explain elastic rebound theory

Explains how energy is stored in rocks

• overtime stresses in the earth build up

• creates a locked fault (a fault that is not slipping because frictional resistance is greater than the sheer stress)

• stress becomes too much (like 4 a levels) the earth breaks

• Rocks bend until the strength of the rock is exceeded

• Rupture occurs and the rocks quickly rebound to an undeformed shape

• Energy is released in waves that radiate outward from the fault.

• generally happen along fault planes or lines of weakness

What are the names of the plates?

seven major and eight minor

Each plate is in motion relative to its neighbours, resulting in geological activity at the plate boundaries. It is also possible, though less common, for geological activity to take place in the middle of plates.

describe and explain rib push/gravitational sliding

Where slab pull is not the main plate driver, ‘ridge push’ is another possibility. As the lithosphere formed at divergent plate margins is hot, and less dense than the surrounding area it rises to form oceanic ridges. The newly-formed plates slide sideways off these high areas, pushing the plate in front of them resulting in a ridge-push mechanism.

How many types of plate boundaries/margins are there? What are they? what occurs at them? Describe and explain

1. Divergent (constructive)

   At divergent plate margins, plates are moving apart and so magma rises through the asthenosphere to the surface of the Earth.

   typically occurs along a mid-oceanic ridge, like the mid-Atlantic rift that extends from the north to the south of the Atlantic Ocean.

   Long chains of mountains form along these ridges. Due to the varying amount and rate of magma released mid-oceanic ridges vary in shape.

   Eruptions along constructive plate margins mainly occur underwater. Pillow lavas are formed as lava is rapidly cooled on the sea floor. In the North Atlantic the extrusion of magma has been so great it created the largest volcanic island in the world, Iceland.

   As magma rises the rocks above often form a dome. The lithosphere is put under great stress and eventually fractures along faults. This forms the underwater rift valleys found along mid-oceanic ridges.

   Rift zones also occur on land and help explain how continents break up. The continental crust must be thin for rifting to happen. One of the best examples is Iceland’s rift valley, þingvellir. This is where the North American Plate and the Eurasian Plate are separating. A graben or sunken valley has been formed where the crust has been stretched, causing faulting.

   East African rift

   Corinth rift- youngest rift

2. Convergent (destructive)

   At convergent plate margins, plates are moving towards one another. They can meet in 3 different ways:

   oceanic-continental (oceanic subducts and this leads to the formation of an ocean trench- the point where the oceanic plate enters the asthenosphere. Continental crust buckles forming an oceanic trench. Sedimentary rock formed on top of the oceanic crust folds upwards along the edge of continental plate. The continental crust also lifts and buckles and magma is injected from the asthenosphere. This process forms fold mountains of which the Andes and the Rockies are examples. As the oceanic crust subducts the continental crust it melts. The magma rises as it is less dense than the material around it. Large intrusions of magma create uplift, further contributing to the formation of fold mountains. Volcanoes are formed where magma reaches the surface of the Earth.

   oceanic-oceanic Where two oceanic plates converge the denser crust subducts the other. This creates a trench. As the oceanic plate descends it melts, and the magma rises forming a volcanic island chain, known as an island arc. The north-west Pacific Ring of Fire has a series of island arcs including the Aleutian Islands.

   continental-continental - Where two continental plates meet there is typically no subduction. Fold mountains, such as the Alps and the Himalayas form.

3. Conservative

   Conservative margins are also known as transform faults.

   At conservative margins, plates slide past each other, so that the relative movement is horizontal, and classified as either sinistral (to the left) or dextral (to the right). Lithosphere is neither created nor subducted, and whilst conservative plate margins do not result in volcanic activity, they are the sites of extensive shallow focus earthquakes, occasionally of considerable magnitude.

   It is possible to see the boundary between plates along a conservative margin. An example of this is the San Andreas fault in California. This is where the North American and Pacific plates slide past each other.

   Transform faults are mainly found on the ocean floor, where they offset mid ocean ridges and enable to ocean to spread at different rates. It was through the work of John Tuzo Wilson that these faults were recognised as the connection between the ocean ridges (divergent margins) and ocean trenches (convergent margins).

What is rifting?

What is a megathrust earthquake and where does it occur?

occur at subduction zones at destructive plate boundaries, the earth’s most powerful with Moment magnitudes exceeding 9.0!!

What are the 3 types of fault?

• normal- the block above the fault moves down relative to the block below the fault

• reverse- the block above the fault moves up relative to the

  block below the fault

• strike-slip- the movement of blocks along a fault is horizontal

  

assess the role of convection currents in the theory of plate tectonics

The asthenosphere behaves like a fluid over very long time scales. There are a number of competing theories that attempt to explain what drives the movement of tectonic plates. Three of the forces that have been proposed as the main drivers of tectonic plate movement are:

• mantle convection currents: warm mantle currents drive and carry plates of lithosphere along a like a conveyor belt

• ridge push (buoyant upwelling mantle at mid-ocean ridges): newly formed plates at oceanic ridges are warm, so they have a higher elevation at the oceanic ridge than the colder, more dense plate material further away; gravity causes the higher plate at the ridge to push away the lithosphere that lies further from the ridge

• slab pull: older, colder plates sink at subduction zones because, as they cool, they become more dense than the underlying mantle and the cooler, sinking plate pulls the rest of the warmer plate along behind it

Research has shown that the major driving force for most plate movement is slab pull, because the plates with more of their edges being subducted are the faster-moving ones. However, ridge push is also presented in recent research to be a force that drives the movement of plates.

How is an earthquake formed?

An earthquake are caused by sudden movements near the Earth’s surface (lithosphere) along a fault (zones of pre-existing weakness in the Earth’s crust)

Movements are preceded by a build-up of tectonic strain, which stores elastic energy in crustal rocks (the lithosphere). This generates a locked fault.

Pressure builds up along the fault which can cause deformation of the lithosphere. 

When the pressure exceeds the shear strength of the fault, the rock fractures causing a rupture and release of energy where rocks jolt past each other.

This produces a sudden release of energy (seismic waves) that radiate away from the point of fracture (hypocentre).

The brittle crust then rebounds either side of the fracture which is the ground shaking; the earthquake felt on the surface. The lithosphere reverts to the original undeformed shape in a new locked fault. 

What are seismic waves? and the four types

Seismic waves can travel both along the surface and through the layers of the earth. There are three types of waves –

P waves (primary) body: cause the immediate shock. Fastest wave. Can move through solid and liquid. Pushes and pulls the rock it moves through

S waves (secondary) body: longer wavelength and arrives seconds later. Can only move through solid rock (this includes the mantle). Moves rock up and down or side to side.

L waves (love): surface wave. Only travel through the crust causing horizontal movement

R waves: also a surface wave- travel just blow or along the ground’s surface, slower than body waves, rolling movement, especially damaging to buildings

Describe liquefaction

The molecules vibrate in both solids and liquids, but in solids they vibrate in place whereas in liquids they have that much more energy so they can slip and slide over each other too. In an earthquake, the molecules in the solid ground are given enough energy that they are no longer required to vibrate just in place, but are also capable of this ‘liquefaction’ – of sliding around and over each other, just like a liquid. Once the seismic waves are spent and there is no more energy being provided, the molecules go back to behaving like a solid

this affects loose rock and sediment. The seismic waves trigger the ground to lose its load bearing capacity, causing large buildings to settle into the ground, tilt and possibly collapse

Why is the Moment Magnitude scale seen as more accurate than the Richter scale

Unfortunately, many scales, such as the Richter scale, do not provide accurate estimates for large magnitude earthquakes. Today the moment magnitude scale, abbreviated M_W, is preferred because it works over a wider range of earthquake sizes and is applicable globally. The moment magnitude scale is based on the total moment release of the earthquake. Moment is a product of the distance a fault moved and the force required to move it. It is derived from modeling recordings of the earthquake at multiple stations. Moment magnitude estimates are about the same as Richter magnitudes for small to large earthquakes. But only the moment magnitude scale is capable of measuring M8 (read "magnitude 8") and greater events accurately.

Magnitudes are based on a logarithmic scale (base 10). What this means is that for each whole number you go up on the magnitude scale, the amplitude of the ground motion recorded by a seismograph goes up ten times. Using this scale, a magnitude 5 earthquake would result in ten times the level of ground shaking as a magnitude 4 earthquake (and about 32 times as much energy would be released). To give you an idea how these numbers can add up, think of it in terms of the energy released by explosives: a magnitude 1 seismic wave releases as much energy as blowing up 6 ounces of TNT. A magnitude 8 earthquake releases as much energy as detonating 6 million tons of TNT.

Magnitude scales can be used to describe earthquakes so small that they are expressed in negative numbers. The scale also has no upper limit. The largest recorded earthquake occurred along the subduction zone in Chile in 1960. It was a magnitude 9.5 but larger earthquakes may be possible. Fortunately, large earthquakes are much less common than small ones.

What is the Modified Mercalli Intensity scale and why is it criticised?

Another way to measure the strength of an earthquake is to use the observations of the people who experienced the earthquake, and the amount of damage that occurred, to estimate its intensity. The Mercalli scale was designed to do just that The original scale was invented by Giuseppe Mercalli in 1902 and was modified by Harry Wood and Frank Neumann in 1931 to become what is now known as the Modified Mercalli Intensity Scale.

Although the Mercalli scale does not use scientific equipment to measure seismic waves, it has been very useful for understanding the damage caused by large earthquakes. It has also been used extensively to investigate earthquakes that occurred before there were seismometers.

Some factors that affect the amount of damage that occurs are:

• the size (magnitude) of the earthquake

• the distance from the epicenter,

• the depth of the earthquake,

• the building (or other structure) design,

• and the type of surface material (rock or dirt) the buildings rest on.

What is the difference between an earthquake prediction and an earthquake forecast?

Probabilities and forecasts are comparable to climate probabilities and weather forecasts, while predictions are more like statements of when, where, and how large, which is not yet possible for earthquakes.

What is an earthquake?

An earthquake is the sudden ground motion or vibration produced by a rapid release of stored-up energy

What is the difference between focus (hypocentre) and epicentre of an earthquake:

The location below the earth's surface where the earthquake starts is called the hypocentre and the location directly above it on the surface of the earth is called the epicentre.

What are benioff zones?

The Benioff Zone of earthquakes is caused by the subduction of one tectonic plate under another.  The earthquakes at the surface boundary between the two plates are shallow.  The subducted plate is forced down deeper causing intermediate earthquakes and as it is forced into the mantle it continues to produce earthquakes (deep earthquakes) until the plate finally is reabsorbed into the mantle at around 700 km or so.

Characteristics of a shallow focus earthquake

Shallow quakes generally tend to be more damaging than deeper quakes. Seismic waves from deep quakes have to travel farther to the surface, losing energy along the way. Shaking is more intense from quakes that hit close to the surface like setting off "a bomb directly under a city,"

Characteristics of a deep focus earthquake

While deep quakes may be less damaging, they're usually more widely felt. Most of the destruction in the Myanmar quake was centered in the tourist town of Bagan where nearly 100 brick pagodas dating back centuries were damaged. At least four people were killed in the Myanmar temblor, which also shattered ancient Buddhist pagodas.

What is a seismometer

A seismometer measures the amount of ground shaking during an earthquake, recording vertical and horizontal movements of the ground on to a seismograph.

Landslide

these occur where slopes are weakened by seismic waves and slide under the influence of gravity

Landslides occur when the shear stress is greater than the shear strength.

70% of all deaths from EQs globally (excluding those from shaking, building collapse, tsunami) are attributable to landslides.

e.g. 2008 Sichuan EQ landslides accounted for 1/3 of all deaths

Shear strength – the force holding the slope together (e.g. lots of trees, shallow slope)

Shear stress – the forces pulling the slope down (e.g. increasing slope angle if building a road)

What is an event profile?

Event profiles can be drawn for any event and help illustrate the great

variation in the nature of tectonic hazards.   They are a common way

to compare and contrast different hazards. The typical earthquake

and volcanic profiles tend to differ most in terms of spatial predictability

and frequency.

What are some changes which decrease stability of slopes?

A decrease in shear strength (upslope forces):

Weathering of rock allows water porosity of rocks  to increase (freeze-thaw cycles) allowing more water to enter.

Weathering also breaks down rocks into new clay which expands when water is present (dry clay is very firm and stable)

Increasing the water content – raises the water table (can increase stress and at the same time decrease strength)

Animals burrowing – allows soil moisture to drain away

Removing vegetation – vegetation binds the soil thus stabilising slopes, the loss of root networks reduces the cohesion of the soil. Slope failures often occur several years after logging, when root systems decay away.

An increase in shear stress (an increase in the forces attempting to pull a mass downslope):

Construction

An increase in slope angle especially at the base of the slope e.g. undercutting for building a road removes the support for the slope

Increasing weight of slope due to increased water content

Shocks and vibrations from earthquakes or machinery – the shaking causes rearrangement of particles, decreasing porosity à water content change from unsaturated to saturated without adding water.

Tsunamis (another secondary hazard) some stats and how do they appear

77% of all deaths in the 2004 Indian Ocean tsunami were women

Tsunami account for 7% of tectonic disasters but 36% of deaths

Three of the top 10 most deadly disasters in recent years were tsunami (2004 Boxing Day - Banda Aceh, Indonesia; 2008 – Sulawesi, Indonesia; 2011 – Tohoku, Japan) – all at the Pacific Ring of Fire.

‘Tsunami’ is a very large wave which floods areas of the coast.

When they are out at sea, they have a very long wavelength, often more than 100km. They are very short in amplitude, at around 1m in height. They travel very quickly often at speeds of up to 700kph, for example taking less than a day to cross the Pacific.

When they reach land, they rapidly increase in height up to over 25m in some cases. They are often preceded by a localised drop in sea level (drawback) as water is drawn back and up by the tsunami. This is often the first warning of its arrival. It slows down as it approaches a land mass but as the frequency of the wave remains the same, so the height of the wave increases greatly

Impacts of earthquake causing land subsidence and uplift- case study

The 2004 Sumatra-Andaman earthquake and tsunami led to significant land subsidence and uplift, which dramatically altered the tidal patterns crucial for mangrove survival. 97% of mangroves in the Nicobar Islands were lost, but these changes did open up new intertidal zones which allowed for mangrove colonisation in previously non-mangrove terrestrial areas

Describe and explain the two causes of tsunamis

Earthquakes

The most common cause of major tsunami is submarine earthquakes occurring beneath the seabed. The earthquake can cause a vertical displacement of the seabed, displacing water upward, which generates a tsunami at the ocean surface. Horizontal displacements of the seabed (strike-slip faults) do not tend to generate tsunami.

Volcanic collapse

These most commonly involve the eruption, or emergence, of a volcanic island. There are two main mechanisms:

1. Flank collapse: the landslide of one side of volcano into the sea, displacing water. This is often accompanied by a lateral blast.

2. Caldera collapse: where the upper part of a volcano collapses, accompanied by a massive steam eruption as water contacts magma.

The 2018 Sunda Strait tsunami (Indonesia) involved a volcano. The island of Anak Krakatoa is formed of a volcano that emerged in the sea from Krakatoa’s crater (which famously erupted in 1883) in 1927. There was a flank collapse during the 2018 eruption created a submarine landslide and tsunami 13m high. There were 435 deaths, 14,000 injured and 3000 homes

How tsunamis occur via earthquakes

Tsunamis

Detection—very difficult to detect in open ocean— because of the small wave height but long wave length. Tsunami waves have no back- only wind driven waves do.

Run-Up - if the first part of the wave to reach the coastline is the wave trough. -There may be a lowering of  sea level below normal this is called DRAWDOWN—if this is recognised then can save lives eg

As the wave approaches land, the waves energy is crowded into a smaller volume of water, therefore waves that were 1m in height in the open ocean may reach 20m

Landfall- death and destruction will depend on what?  Land uses, population density, warning given, geography and relief of coastal areas

Hydrostatic- objects like boats and vehicles are lifted and carried inland.  Same could occur with a backwash/rundown

Hydrodynamic- tearing of buildings apart, washing away soil, undermining foundations

Shock effects- battering by debris carried in the wave—human deaths result from drowning, hit by moving debris, lifted and battered.

Hazard hits quickly and unexpectedly but prolonged—no time to think through properly in responses- so danger wasn’t recognised

Looks like a normal wave at first BUT on reaching land , breaks and floods due to one wave with no back

Occur from earthquakes of magnitude > 6.5

Occur when the focus has a depth of < 50km

90% occur in Pacific

Over 25% occur in the Japan-Taiwan island arc (the most active source area)

Between 1900 – 1980, 370 tsunami were observed in Pacific

The greater the tsunami run up (wave height above sea level) the greater the devastation but the less frequent

If the first part of the wave to reach the coastline is a wave trough, there may be a lowering of sea level below normal levels, called a drawdown.

Human factors affecting vulnerability to tectonic hazards

Population density

Awareness

Cultural factors affecting public response

Access to education Regardless of level of development people can be educated to survive natural hazards.  Education about the risks of contaminated flood water or Earthquake drills (like the ones Japan has on the 1st September to commemorate the 1923 Tokyo Earthquake) can save many lives.

Lines of communication

Early-warning system

Emergency service

Building codes many HICs have laws that prevent building in hazardous locations, along a low coastline at risk from storm surges in a hurricane for example.

Insurance

Physical factors affecting vulnerability to tectonic hazards

Rock type generally earthquake shaking in soft sediments is larger and longer than when compared with the shaking experienced at a "hard rock" site. Softer sediments are more likely to liquefy too, which can contribute to building collapse.

Magnitude the size of the event massively affects the impact it has.  A hurricane of magnitude 5 on the Saffir Simpson scale will have more impact than that which has a magnitude 3, whilst every step up the Earthquake Richter scale represents a 10 fold increase in damage and a 30 fold increase in energy released.

Frequency this is how often the hazard occurs.  The more often a hazard occurs generally the more prepared people are, and the more used to coping they are.  Large earthquakes and volcanic eruptions are generally very rare events in terms of a human lifespan so when they occur they can surprise.  Floods are often regular events, large parts of Bangladesh flood every year for example. In this event people can adjust their buildings and lives to cope with the risk associated.

Time since the last hazardous event the amount of time since the last hazardous event can influence the impact, if a long time goes by people can be unprepared. Also, if the hazard occurs when lots of people are asleep they can also be unprepared. The Christchurch Earthquake of 2011 happened during the day when lots of people were at work, this contributed to the death toll as many got trapped in collapsed office buildings.

Location of epicentre

Time of day

Duration of shaking

Depth of earthquake

Relief of the land

2002 Eruption of Mount Nyiragongo, Democratic Republic of the Congo 

General information: 

• Divergent plate boundary on the East African Rift (African Plate splitting into the Nubian Plate and the Somali Plate); on the border of DRC and Rwanda 

• Height of 3470m; 2000m above a rainforest, approximately 15km from city of Goma (population approximately 700,000) 

• Opening is 1.2km in diameter, 600m deep lava lake at 1000⁰C, largest in the world 

2002 eruption: 

• 17^th January 2002, 09:30, lasted roughly 24 hours 

• 147 deaths reported by the UN, 60-100 of whom died in the explosion of Goma Central Petrol Station 

• 470 people suffered burns, fractures, gas intoxication 

• 14,000 homes destroyed, 30,000 people displaced 

• Up to 350,000 fled from the lava flows (covering 13% of the city) to Rwanda 

Impacts: 

• CO2 seeping from rock pores endangers settlements into the future 

• Lack of toilets mean ‘long-drop’ toilets are necessary, allowing the spread of cholera 

• Digging toilets and graves in the rock is nearly impossible 

Responses: 

• US gave $50,000 to DRC and Rwanda; $5 million to NGOs and the UN for disaster aid; wool blankets, water, dust masks, plastic sheeting (for shelter) worth over $800,000 

• Caritas (disaster relief NGO) Goma distributed food and relief for 15,000 families 

• ECHO (European Civil Protection and Humanitarian Aid Operations) gave €5 million 

• Concern Worldwide, UN/UNICEF, governments of 24 nations all donated 

Current monitoring strategies: 

• Lava characteristics can’t be directly tested as samples are too hot and the journey to the crater is treacherous 

• A volcanic observatory was established 

• ‘Goat Test’ to test CO2 levels 

• Time lapses on camera traps to measure changing level of lava lake which can show pressure changes in the magma; hard to see past smoke, harsh conditions bad for camera 

• Practice eruption drills for the population 

• SO2 levels monitored by gas box; unreliable as they depend on weather and wind direction 

• Analysis of lava bombs give information about lava for future eruptions 

• Microphones pick up low-frequency infrasound and monitor lava lake pressure changes 

 

Deggs model

Degg’s model shows the overlap of natural hazard and human vulnerability.

The greater the scale of a earth process or event and the more vulnerable and exposed the people, the greater the scale of the natural hazards or disaster.

Earthquake predictions and problems

• satellite geodesy- measure how the earth is deformed

• good at knowing where earthquakes occur but not why

• a useful prediction= size and level of damage, where and when

• US geological survey locates about 55 every day

• occur because of nucleation on slip on faults typically 20-30km deep

• Neither the USGS nor any other scientists have ever predicted a major earthquake

• how much force has been building up on the rock is unknown

• we don’t know what the critical point of release is

• some EQs have pre-cursors e.g. foreshocks, radon gas release, changes in animal behaviour but these are not consistent and only recognised as a precursor afterwards!

• Japan, 2011 ground moved by 50m! as a result of the release of elastic energy

Examples of modifying the event strategies

Land use zoning- prevention of buildings on low-lying coasts (tsunamis), avoiding areas close to volcanoes, avoiding areas where liquefaction is likely

Benefits- low cost, relocates people from areas of high-risk

issues- prevents economic development in some coastal areas, requires strict enforcement

Aseismic buildings- cross-bracing, using counterweights, deep foundations e.g. Hawaii timber houses> can be moved easily

Benefits- protects people and property, financially possible in the developed world, basic design can be replicated in the developing world.

issues- high costs for tall buildings, older buildings and homes for people on low incomes are too difficult to protect

Tsunami defences- building sea walls and breakwaters

benefits- reduces damage, provides a sense of security

issues- can be overtopped, very high cost, unsightly

Tsunami resistant designs

• Mangrove swamp and coral reef protection

• Build buildings at a higher level far from the shoreline and not at the top of a smooth shallow beach

• If buildings are high, then water can flow under them

• It helps if the building is not square on to the wave front. If diagonal, the wave hits the pointed corner first and is diverted around the sides. Pressure is much reduced. Buildings should not be close together in a way that makes a wider dam. If roads have buildings all along both sides, the water is funnelled along the roadway, accumulating debris as it goes, and with no reduction in height or destructive force. It is much better if gaps are left between buildings out through which the water can dissipate. If the soil is sandy, then the footings should be deep and bracing should go right down to the feet. Light soil will also be protected from erosion by tarmac or concrete surfacing, which should go right underneath the floor if it is raised.

• Timber buildings are much liked in earthquake areas because they are light and thus reduce earthquake effects. But they are the worst possible choice in tsunami-prone areas; like the ships, they float, and there is nothing to hold them down. The wood becomes weapons which destroy buildings and lives.

Lava diversion- channels, water cooling e.g. 1973 Eldfell, 2024 Blue Lagoon, 1983 Etna

Benefits- diverts lava away from people and buildings, relatively low-cost

issues- only works for basaltic lava, not feasible for majority of explosive volcanoes

Cry wolf syndrome

occurs when predictions prove to be wrong so that people are less likely to believe the next prediction and warning and therefore fail to evacuate

e.g. l’Aquila, Italy 2009- Scientists charged with manslaughter for failure to warn people

Earthquake kits

Governance

the sum of the many ways individuals and institutions, public and private, manage their common affairs. This involves negotiating responses to problems that affect more than one state or region.

Reason’s Swiss Cheese Model

really good in a conclusion

Modify the vulnerability and resilience strategies

HI tech

e.g. Sakurajima Japan

Community

e.g. 1997 Montserrat

1st September every year in Japan- Disaster Preparedness Day

Shakes out 3rd Thursday of October in California

Modify the loss strategies

Assess the importance of prediction and forecasting in reducing the vulnerability of communities to earthquake hazards. (12)

Factors affecting vulnerability Nepal 2015

Factors affecting vulnerability Japan 2011

Factors affecting vulnerability Haiti 2010

Assess the importance of governance in the successful management of tectonic mega-disasters

Intro: Define tectonic mega-disasters, What is management in relation to tectonics? consider both sides of why governance is good and why it can be bad, BLUF- Other factors such as physical can play a role but governance is most important alongside development- could put that in conclusion. Management involves preparation, prediction, prevention, damage control, and repair after the disaster. A good government is involved in each of these.

define coping capacity and vulnerability

1. Preparation

How a government helps- Japan- modify Vulnerability, building codes up to date unlike Haiti, community preparedness

How a government is not important-

1. Prediction

How they help-

How they are not important- We cannot predict Earthquakes, and some governments may have less advanced prediction technology

1. After the disaster

How they help- modify the loss through secondary effects e.g. cholera in Haiti

How they aren’t important-

1. Corruption versus Non-Corruption

   For example in Haiti there is a corrupt government that lacks funding, especially after the 2011 earthquake that caused damage to 120% of their GDP they would rely on other countries for repairs

2. Repair and good relations with neighbouring countries can gain aid in an immediate response

   With the 2008 Sichuan earthquake, the Chinese government helped with the development of education of hazards and immediate response to manage the disaster

3. On the other hand, managing tectonic disasters

Conclusion

What is a volcano?

A landform that develops around a weakness in the Earth’s crust from which molten magma, volcanic rock, and gases are ejected or extruded.

What is the volcanic explosivity index (VEI) ?

the volcanic explosivity index (VEI) is a relative measure of the explosiveness of volcanic eruptions. It is a composite index that combines eruption height, volume of material erupted, and duration of eruption.

Events of VEI 6 and over are very rare e.g. Tambora 1815, Yellowstone Caldera 600,000 years ago

1-8 (no modern human has ever experienced a VEI of 8- 1815 most recently 7.6km Mount Tambora, Indonesia- ash cloud circulated whole globe- 3 years of darkness, crop failure, pyroclastic flows killed people immediately)

Hunga-Tonga 2022- VEI 6

0-3/4 associated with shield volcanoes and basaltic eruptions at constructive plate margins and mid-plate hotspots Eyjafjallajokull VEI 3

Subduction zones have a high VEI of 3 or 4 because their magma has a high gas and silica content.

4-7 occur at destructive plate margins, erupting high viscosity, high gas, high silica, andesitic/rhyolitic magma, Merapi 2010 VEI 4

The higher explosivity VEIs are less common because the magma chamber has to fill up before eruption e.g. Yellowstone

Describe the global distribution of volcanoes

There are about 1500 active volcanoes and about 50 of them erupt annually. Volcanic hotspots, such as the Ring of Fire, are also situated amongst the centre of pates. This is a localised area of the lithosphere (Earth’s crust and upper mantle) which has an unusually high temperature due to the upwelling of hot molten material from the core. (First theorised by Tuzo Wilson in 1963) ➔ At hotspots, such as the Hawaii hotspot, magma rises as plume (hot rock).

Volcanoes are primarily distributed along tectonic plate boundaries, with the majority found in the "Ring of Fire," a horseshoe-shaped zone surrounding the Pacific Ocean. This region accounts for about 75% of the world’s active and dormant volcanoes due to subduction zones. Other significant areas include mid-ocean ridges (e.g., Iceland), rift valleys (e.g., East African Rift), and hotspots (e.g., Hawaii and Yellowstone).

Volcanoes are mainly distributed along tectonic plate boundaries- the majority (75%) are located in the Ring of Fire but there are significant areas across mid-oceanic ridges such as Iceland, hotspots such as Yellowstone and Hawaii which are in the centre of plates and rift valleys such as the East African rift. There is a cluster of volcanoes in Indonesia and Japan along the destructive plate margin.

Hazard profiles

Tectonic events can be compared using hazard profiles. These allow a better understanding of the nature of hazards, and therefore risks associated which each. For example, there may be a continuous line ranging from least to greatest (for example, short to long with duration), with each hazard event located on this line (in relation to their duration in this example.) It gives more information than just ranking them, since it shows the difference between each event, and can be used to compare multiple aspects of different

hazards (or different types of the same hazard, e.g. volcano).

Successful evacuation case study

Mount Pinatubo 1991- killed 800, 25,000 were evacuated

What are the three types of magma?

1. Basaltic magma

   • has low viscosity is hot 1200 celsius degrees and runny like warm treacle, has a lower silica content, takes a longer time to cool and solidify so flows considerable distances as rivers of molten rock, produces extensive but gently sloping landforms- shield volcanoes- non violent eruptions, eruptions are frequent but relatively gentle, lave and steam ejected, found at constructive plate margins where magma rises from the mantle, e.g. fissures along the Mid-Atlantic Ridge (Heimaey); over hot spots (Mauna Loa, Hawaii)

   • low vei

2. Andesitic magma/ acid lava

   • viscous, les shot 800, flows more slowly and for shorter distances

   • larger silica content

   • soon cools and solidifies, flowing very short distances, produces steep sided, more localised features, eruptions are less frequent but violent due to the build up of gases

   • as rocks, gases, steam and lava ejected

   • found at destructive margins where oceanic crust is destroyed (subjected), melts and rises, e.g. subduction zones Mount St Helens and island arcs Mt Pelee

   • stratovolcanoes- Piantubo 1991, Phillipines

   • plume penetrates into the the troposphere

   • get pyroclastic flows on the side and tephra fallout

3. Rhyolitic magma

   • high gas content

   • catastrophic eruptions

   • high viscosity, which traps the gas and builds pressure

   • high vei

   • high silica content

What is a lateral blast?

Lateral eruptions are caused by the outward expansion of flanks due to rising magma. Breaking occurs at the flanks of volcanoes making it easier for magma to flow outward. As magma is pushed upward towards the volcano it diverges towards the flanks before it has a chance to erupt from the crater. These are super difficult to predict. Can also get a pyroclastic flow happening. E.g. Mount St Helens, Mt Pelee.

Hazard profiles of different hazards

Basaltic shield eruption

Magnitude: small

Speed of onset: fairly slow

Areal extent: local

Duration: fairly long

Frequency: quite high

Spatial predictability: fairly precise

Andesitic composite cone eruption

Magnitude: almost middling

Speed: middling

Areal extent: closer to local than regional

Duration: medium

Frequency: fairly low

Spacial predictability: fairly precise (but less so than basaltic shield)

Subduction zone earthquake​

Magnitude: more than medium

Speed: very rapid

Size: closer to regional than local

Duration: shortest

Frequency: closer to low than high

Spatial predictability: fairly random

Tsunami

Magnitude: largest

Speed of onset: rapid

Areal extent: largest

Duration: quite short

Frequency: high

Spatial predictability: highest

How does silica content affect viscosity?

The higher the lava’s silica content, the higher its viscosity.

Two types of volcanoes?

shield and composite/cone

Composite/cone volcano

examples

plate boundary

type of magma

type of eruption

material ejected

frequency of eruption

Mt St Helens and Pinatubo

Andesitic magma, which is lower in temperature, has more silica and a lot of dissolved gases and is more likely to explode when it reaches the surface. or andesitic

Located at destructive plate margins

Acidic lava, which is very viscous (sticky).

Steep sides as the lava doesn't flow very far before it solidifies.

Alternate layers of ash and lava. For this reason, they're also known as stratovolcanoes as Strato means layers.

Violent eruptions- lava shatters into pieces

lava bombs, ash and dust

Longer periods between eruptions. from time to time-long dormant periods

Shield volcano

examples

plate boundary

type of magma

type of eruption

material ejected

frequency of eruption

Shield volcanoes are found on divergent/constructive plate boundaries, where two plates move away from one another. Shield volcanoes have the following characteristics:

• Mauna Loa, Hawaii, Eyjafallajokull, Iceland

• basaltic magma, which is high in temperature, very low on silica and with low gas content - this type of magma produces fluid lava with very little explosive activity

• basic lava, which is non-acidic and very runny

• gentle sides as the lava flows for long distances before it solidifies

• constructive plate margins

• no layers, as the volcano just consists of lava

• less violent eruptions- effusive- gas escapes easily

• mainly lava rather than other materials.

• shorter periods between eruptions

Mount St Helens (1980) Case study (Unsuccessful management)

• cone volcano

• no lived experience of an eruption

• 5 mile exclusion zone

• Earth tremor caused by liquid rock moving a mile below

• The tremor triggered the biggest landslide ever recorded- 8000 million tonnes of rock

• Lateral blast due to release of pressure 670mph

• ash cloud of heat 12 miles high- boiled sap in trees and uprooted them

• not a single tree left within 6-mile radius

• Melted glaciers- created fast-moving mudflows- jokulhlaups- meltwater- 100mph

• Sunday morning= lower death toll- good time of day-people were’’t up on the mountain yet 8:32 am

• lost 1300 feet from its summit

• 540 million tonnes of volcanic ash as far as 550 miles away- 2 weeks circled the entire globe

• 57 people were killed- all but 3 outside of the red zone

Mount Nyiragongo, Congo Case Study (LIC)

• high pop density

• fertile land

• one of the most dangerous volcanoes on earth

• Divergent plate boundary on the East African Rift (African Plate splitting into the Nubian Plate and the Somali Plate); on the border of DRC and Rwanda 

• Height of 3470m; 2000m above a rainforest, approximately 15km from the city of Goma (population approximately 700,000) 

• Opening is 1.2km in diameter, 600m deep lava lake at 1000⁰C, largest in the world 

2002 Eruption

• 17^th January 2002, 09:30, lasted roughly 24 hours 

• 147 deaths reported by the UN, 60-100 of whom died in the explosion of Goma Central Petrol Station 

• 470 people suffered burns, fractures, gas intoxication 

• 14,000 homes destroyed, 30,000 people displaced 

• Up to 350,000 fled from the lava flows (covering 13% of the city) to Rwanda 

Impacts

• CO2 seeping from rock pores endangers settlements into the future 

• Lack of toilets means ‘long-drop’ toilets are necessary, allowing the spread of cholera 

• Digging toilets and graves in the rock is nearly impossible 

• The primary effects – The speed of the lava reached 60kph which is especially fast. The lava flowed across the runway at Goma airport and through the town splitting it in half. The lava destroyed many homes as well as roads and water pipes, set off explosions in fuel stores and powerplants and killed 45 people

• The secondary effects – Half a million people fled from Goma into neighbouring Rwanda to escape the lava. They spent the nights sleeping on the streets of Gisenyi. Here, there was no shelter, electricity or clean water as the area could not cope with the influx. Diseases such as cholera were a real risk. People were frightened of going back. However, looting was a problem in Goma and many residents returned within a week in hope of receiving aid.

Responses

• US gave $50,000 to DRC and Rwanda; $5 million to NGOs and the UN for disaster aid; wool blankets, water, dust masks, plastic sheeting (for shelter) worth over $800,000 

• Caritas (disaster relief NGO) Goma distributed food and relief for 15,000 families 

• ECHO (European Civil Protection and Humanitarian Aid Operations) gave €5 million 

• Concern Worldwide, UN/UNICEF, governments of 24 nations all donated 

Current monitoring strategies

• Lava characteristics can’t be directly tested as samples are too hot and the journey to the crater is treacherous 

• A volcanic observatory was established 

• ‘Goat Test’ to test CO2 levels 

• Time lapses on camera traps to measure changing level of lava lake which can show pressure changes in the magma; hard to see past smoke, harsh conditions bad for camera 

• Practice eruption drills for the population 

• SO2 levels monitored by gas box; unreliable as they depend on weather and wind direction 

• Analysis of lava bombs give information about lava for future eruptions 

• Microphones pick up low-frequency infrasound and monitor lava lake pressure changes 

Volcanic hazards: primary and secondary + case studies

• Lava flows and lava domes

  • Lava flows are flows of magma extruded onto the surface of a volcano. It is rare for lava to cause the direct loss of life as it flows very slowly- people can evacuate, e.g. The Blue Lagoon 2024. The viscosity increases with silica content. Low-viscosity lava types can flow much further distances.

  • Lava domes form when high-viscosity lava is slowly erupted from a volcano. Due to the high viscosity of the lava, it cannot travel far from the vent and a dome of lava builds up. These lava domes are particularly hazardous as they tend to be unstable and can collapse, causing pyroclastic density currents.

  • Flood basalts: the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava rare form of lava flow- our understanding of these is based on studies of past eruptions like the Deccan Traps in India. hey can have thicknesses up to a kilometre and release large amounts of gas; they can cause air pollution and even have an impact on the global climate. In 2014, the Holuhraun fissure eruption reached flood basalt size. It is now the largest flood basalt in Iceland since the Laki eruption in 1783–1784, which caused the deaths of about 20 per cent of the Icelandic population by environmental pollution and famine. It most likely also increased levels of mortality elsewhere in Europe, through air pollution by sulphur-bearing gas and aerosols.

• Pyroclastic flows

  • Hot density currents consisting of mixtures of rock debris and gas that flow along the ground at high speed.

  • they move as a result of gravity

  • their extreme power and energy has been shown through some pyroclastic flows Defying Gravity and moving uphill.

  • They typically move at 110 km per hr or faster down the sides of volcanoes

  • Fountain collapse pyroclastic flows- can occur during explosive eruptive activity, where the mixture of gas and ash emitted from the volcano is too dense to rise buoyantly into the atmosphere. Instead, it collapses around the volcano

  • Dome collapse- pyroclastic flows- volcanoes that erupt very viscous lavas that form domes can also produce pyroclastic flows if the dome becomes unstable. pyroclastic flows are produced when large portions of the dome collapse and disintegrate

  • Temperatures may exceed 400ºC

  • For example, during the 1902 eruption of Mont Pelee in Martinique (West Indies), a pyroclastic flow (also known as a “nuee ardente”) demolished the coastal city of St. Pierre, killing nearly 30,000 inhabitants.

• Lahars

  • snow and ice melt on top of the volcano, meltwater mixes with the ash, causing a mudflow

  • Eruptions cause static energy resulting in thunderstorms. The rain mixes with the ash Nevado del Ruiz, 1985

  • It is a Javanese word for a type of volcanic mudflow made up of volcanic debris and hot or cold water.

  • They move at speeds that range from less than 10kmph to up to tens of kilometres per hr.

  • As they flow down river valleys they can gather more and more loose material.

  • These can be viscous and non-viscous

  • Notable lahars include those at Mount Pinatubo in the Philippines and Nevado del Ruiz in Colombia, the latter of which killed more than 20,000 people in the Armero tragedy.

• Jökulhlaup

  • an Icelandic word that is used to describe a glacial outburst flood- a sudden release of water from a lake that lies under or close to a glacier. yo-KOOL-lahp

  • Eyjafjallajökull in 2010

  • One of the triggers of a jökulhlaup could be the eruption of a volcano situated beneath a glacier that melts overlying ice or weakens a dam made of glacial moraine sediments. The sudden removal of the lake dam releases a huge volume of water to produce a megaflood that can wash away roads and bridges.

• landslides and debris avalanches

  • can be triggered as the result of a volcanic explosion or dome collapse, especially when heavy rainfall is common

  • Debris avalanches tend to become channelled into valleys

  • it is difficult to reduce the impact of debris avalanches because they can occur without warning- even on dormant volcanoes!

  • once initiated it is almost impossible to evacuate areas in the paths of debris avalanches because of the great speed with which they travel.

  • On Boxing Day 1997, a large volcanic explosion caused the partial collapse of the Soufrière Hills Volcano, Montserrat, triggering a debris avalanche. About 60 million m³ of dome and crater wall travelled to the south as a debris avalanche with other pyroclastic material. The villages of St Patrick’s and Morris were swept away in less than 30 minutes.

• tephra/ashfall

  • tephra is an umbrella term for all erupted clasts regardless of size

  • Ash describes particles of less than 2mm in size

  • During an eruption most tephra falls to the ground around the volcano- this affects nearby buildings and travel.

  • The loading of tephra on plants can lead to branches being stripped or plants being buried- this can have an impact on agriculture

  • volcanic ash is easily transported by winds to hundreds of thousands of kilometres away. Sometimes it reaches the stratosphere.

  • Ash is made up of small, sharp, angular fragments of glass and other volcanic rock; due to its abrasive nature, volcanic ash can cause damage to aircraft.

  • 18 May 1980, Mount St. Helens

  • spreading five hundred million tons of tephra ash

• release of gas

  • Various gases can be emitted by active volcanoes before, during or after an eruptive event and can cause various health hazards locally, but also have the potential to affect the climate globally.

  • The main 5 gases posing a threat to health are: carbon dioxide, hydrogen chloride, hydrogen fluoride and sulphide and sulphur dioxide

  • People are exposed to harmful volcanic gases by breathing them in or through contact with eyes and skin. These are very hazardous because they cannot be seen, they are denser than ambient air and, therefore, can be ponded in depressions around an active volcano. Sulphur gases convert to sulphate aerosols which if they reach the stratosphere may remain there for years, causing short-term climate change.

  • The 1991 eruption of Mt. Pinatubo is thought to have injected more than 250 megatons of gas into the upper atmosphere on a single day

• tsunamis

  • means harbour wave- Japanese word

  • can form in relation to many things

  • volcanoes can cause tsunamis even tho they are less common

  • Tsunamis have caused the most fatalities associated with volcanic eruptions in historical times

  • Tsunamis form when water is placed- on volcanoes- this can occur via several mechanisms e.g. a submarine eruption, collapse of part of a volcanic edifice, entrance of lahars or pyroclastic density currents into the surrounding water.

  • An example of such an event is the 1883 eruption of Krakatau, Indonesia. While there is still some discussion as to the exact source of the tsunamis, the eruption produced large pyroclastic flows and led to collapse of the volcano. Numerous tsunamis were produced, with the most devastating resulting in more than 36 000 deaths.

  • In December 2018, approximately half of the volcano collapsed into the surrounding seas, forming a tsunami that affected much of the coast along the Sunda Straits and causing the deaths of more than 400 people.

Volcano management techniques

• prediction

Can you always pretend a volcanic eruption?

Prediction is getting better, but there are a small number of unpredicted eruptions, e.g. Whakaari New Zealand 2019, Mount Ontake Japan 2014- 62 people died.

Most unpredicted eruptions are phreatic- instantaneous eruptions of gas, steam, ash, lava and volcanic bombs caused when groundwater contacts magma either magma migrating up to a groundwater layer or water migrating down to magma. The Eyjafjallajökull eruption in 2010 was phreatomagmatic as a result of magma erupting under ice – this was an unusually explosive eruption (VEI 4) for a constructive plate margin that is often much more effusive due to the interaction of the magma creating gas and steam – the ice acted as a type of ‘catalyst’.

Phreatic eruptions are more common at subduction zones where it is thought sea water may be interacting with magma due to subduction.

Frequency since last eruption can affect prediction e.g. La Palma

Modify the event (protection)

• Hazard-resistant designs (timber houses in Hawaii) Ash fallout has a large impact and design can help reduce this- this prevents the buildup of ash on roofs.

• Building design can’t really control the stronger hazards like pyroclastic flows

•Environmental control, e.g. lahar barriers- significant dangers are posed by the secondary effects of lahars- in Indonesia some villages have artificial mounds to enable villagers to escape higher ground, although adequate warning is needed if this is to be effective because of their rapid onset

• draining crater lakes (Kelud, Java)- a tunnel through the crater wall of Kelut volcano, Java- has also been tried to drain the crater lake and reduce the risk of lahars forming. A notch was built through the crater wall of Mount Pinatubo to drain a lake which developed in the years after its big eruption.

• artificial mounds (Hilo, Hawaii)- proposed to protect Hilo, Hawaii from future lava flows. In Indonesia, some villages have these to enable villagers to escape to higher ground. ). After the 2002 Nyiragongo eruption in the DRC, artificial mounds of earth were used to elevate the land.

• explosives (1983 Etna) -       Explosives used with some success in 1983 eruption of Etna when 30% of slow moving lava was diverted from its course. The USGS scientists and US military worked in partnership with the Italian government to execute this

• water spray (1973 Eldfell) -       Sea water sprays were successfully used to cool lava flows in 1973 eruption of Eldfell, Iceland to protect harbour. They successfully protected the harbour of Vestmannaeyjar.

•Land-use zoning: avoiding areas close to volcanoes

Modify the loss (response)

1.        Aid: Technical aid supplied by MEDC for monitoring equipment. Financial aid used during and after event. Government must be willing to ask for and accept from others. . Aid for volcanic hazards comes in two forms: technical aid for monitoring and forecasting and financial / goods aid. Technical aid is usually supplied by MEDC experienced in volcanic eruptions – e.g. the USGS helped with Pinatubo. This involves the use of high cost monitoring equipment and expertise to try to forecast events. Financial and other aid is used as a strategy during and after an eruption. This may need to occur over a long period compared with other natural hazards, since eruptions may continue for months at varying levels of activity. For aid to be an effective management approach governments must be willing to ask for and receive help from other nations. Indonesia has much experience with volcanic eruptions and has developed a high level of hazard mitigation within its financial resources. This involves monitoring of volcanoes and planning for how aid will be used. The Tungurahua volcano eruption in Ecuador in 2006 Japan, Spain, Switzerland, China, Britain, Bolivia, Peru and the United States have jointly provided 1.4 million U.S. dollars for the volcano victims.

2.        Insurance: Insurance companies need to identify key areas of risk and hazards in order to secure their business. Indonesia developed high level of hazard mitigation. Monitors volcanoes and plans how aid will be used. In richer areas, people are urged to take out insurance to cover their losses, the only problem being that for individuals, this is very expensive. In the Kobe earthquake in Japan in 1995, for example, only seven per cent of the people were covered by earthquake insurance.

 

Modify the vulnerability (prediction/preparation)

1.        Community preparedness - Most volcanic events are preceded by clear warnings of activity from the volcano. If the community at risk is prepared in advance, many lives can be saved. Evacuation is the most important method of hazard management used today. Evacuation of the area at risk can save lives, but advance preparation and management structures to organise the evacuation, temporary housing, food etc. are needed.

-       Evacuations: The length of time of the evacuation may be long term: e.g. 5000 residents of Montserrat were evacuated three times between December 995 and August 1996 for periods of up to three months, to avoid pyroclastic flows and ashfalls. By November 1996, the disruption was thought to last another eighteen months. The scale of evacuations can be huge – in 1995 volcanologists and civil defence officials drew up an emergency plan for the 600,00 people at risk from an eruption of Vesuvius. The operation is large scale and involves removing people to safety by ship. If the people involved panicked the plan would be useless. People need to be clear of the risk and how to behave during an event.

Evacuations have been very successful in recent times and are the most common hazard-management strategy. Pinatubo had the evacuation of 250,000 people but 800 still died. Nevado del Ruiz was a disaster with 23000 deaths as the Colombian government did not have a policy in place for monitoring volcanoes and for disaster preparedness. Communications between scientists monitoring volcanoes and government officials must be clear, consistent and accurate. The eruption was expected, and scientists monitoring the activity had produced a hazard map. However, a lack of clear communication and indecision resulted in disaster. The Colombian government had more serious and immediate problems – economic crisis, political instability and drug gangs (narcotic cartels) – to deal with. Hazard salience is important at the government level.

-       Prediction and warning: Knowledge of volcanic processes is incomplete, but there have been great strides made in forecasting eruptions. Various physical processes can be monitored for changes which can signal an impending eruption. The record of past eruptions is also used to help determine what and where the risks are highest. At the present time, only 20% of volcanoes are being monitored. As might be expected this is mainly in MEDCs such as Japan and the USA which have the researchers, technology and cash to undertake these activities. Even in these areas records are not complete. An example of a closely monitored volcano is Sakurijama, in South Kyushu, Japan.

In countries lacking the financial and technological resources for such monitoring, more basic but still useful techniques have been used. In the Philippines, local people are trained to look out for early-warning signs such as sulphur odours, steam releases and crater glow.

Once scientists have detected signs of activity the events must be interpreted to produce a hazard assessment and prediction of what will happen. Only then can government officials and other agencies such as the news media be informed and warnings and evacuation be introduced to the general public. This is still difficult to do accurately, and interpretations may differ among the scientists involved. This was to some extent the case with Nevado del Ruiz and led to the delay of the warning to the Colombian government, although the hazard map eventually produced was very accurate. The ashfalls were confined to the marked areas and the valleys like the Lagunillas (leading to Armero town) were affected by lahars as predicted.

Volcanoes often show signs if impending eruption and monitoring can be increased as the volcano becomes active.

2.        Volcanic hazard mapping: Places with less money, look for signs  instead e.g. steam releases. Do hazard assessment and predict what will happen. However interpretations may differ, causing delay etc.

3.        Land use planning: Land use can be planned once there is an agreed volcanic hazards map to use as a basis. It is still difficult to predict in the long term the timing and scale of future eruptions. Many LICs do not possess the maps and past records necessary to produce accurate hazard assessments, but where they do exist they can be used to plan land-uses which avoid high risk areas or would result in reduced economic losses. These need to be enforced through legislation and education of the public.     

Example of successful management

What opportunities did the eruption of Eyjafjallajokull bring?

Despite the problems caused by the eruption of Eyjafjallajokull, the eruption brought several benefits. According to the Environmental Transport Association, the grounding of European flights prevented some 2.8 million tonnes of carbon dioxide into the atmosphere (according to the Environmental Transport Association).

As passengers looked for other ways to travel than flying, many different transport companies benefited. There was a considerable increase in passenger numbers on Eurostar. It saw a rise of nearly a third, with 50,000 extra passengers travelling on their trains.

Ash from the Eyjafjallajökull volcano deposited dissolved iron into the North Atlantic, triggering a plankton bloom, driving an increase in biological productivity.

Following the negative publicity of the eruption, the Icelandic government launched a campaign to promote tourism. Inspired by Iceland was established with the strategic intent of depicting the country’s beauty, the friendliness of its people and the fact that it was very much open for business. As a result, tourist numbers increased significantly

Example of unsuccessful management

Nevado del Ruiz, 1985

• lack of aid

• bad preparation

• 100 years ago was a previous eruption

• no lived experience

• scientists warned locals 2 months before

• local authorities disregarded evacuation orders as concerned about damaging property prices

• many killed outright by the mudflow

• 1000 survivors still buried in the mud

• rescuers lacked vital tools and equipment to get people out of the mud- journalists appeared but not equipment

• water pump broken

• 25,000 victims left in mud

Why do people live in a hazardous area?

• emotional attachment

• always lived there

• roots

• ignorance of the risks/underestimation

• lack of alternatives

• economic opportunities like tourism, farming, mining, geothermal power

Seismic Gap Theory

• 'Seismic gaps', i.e. areas that have not experienced an earthquake for some time and are 'overdue' can point to areas of high risk

Definitions of a disaster

-Situation or event, which overwhelms local capacity, necessitating a request to national or international level for external assistance

An unforeseen and often sudden event that causes great damage, destruction and human suffering. Though often caused by nature, disasters can have human origins.

The International Disaster Database defines disasters as situations or events which overwhelm local capacity, necessitating a request for external assistance at the national or international level. Disasters are unforeseen and often sudden events that cause significant damage, destruction, and human suffering. To qualify as a disaster, it must have at least one of the following criteria:

• 10 fatalities;

• 100 affected people;

• a declaration of state of emergency;

• a call for international assistance

Define a natural hazard

-Threatening event, or probability of occurrence of a potentially damaging phenomenon within a given time period and area.

-Without people it is just a natural event not a hazard, it needs the interaction of people to make it a hazard!

Define risk

Expected losses (of lives, persons injured, property damaged and economic activity disrupted) due to a particular hazard for a given area and reference period. Based on mathematical calculations, risk is the product of hazard and vulnerability.

Define vulnerability

Degree of loss (from 0% to 100%) resulting from a potential damaging phenomenon.

describes how susceptible a population or parts of a population are to the damage of hazards, notably “the characteristics of a person or group and their situation that influence their capacity to anticipate, cope with, resist and recover from the impact of a natural hazard.”(Wisner, Ben et al 2005, 11)

is determined by processes in the natural environment and by places, people and power.

tends to increase the lower the country’s economic development and socio-political stability because risks and vulnerability make the impact of natural hazards patterns worse.